We have investigated the optimal conditions for molecular beam epitaxial growth of high quality GaN on 6H-SiC(0001) substrates. The quality of these films is reflected both by the narrow x-ray peak widths as well as the excellent surface morphology. In this work, it is shown that increasing growth temperature leads to an improvement in bulk quality and lower x-ray peak widths for both symmetric and asymmetric reflections. We also note a marked improvement in surface morphology, from a columnar appearance to a two-dimensional surface, under extremely Ca-rich growth conditions.